Gut Organogenesis
The G.I. tract is developed from epithelial tissues derived from the endoderm. The fore, mid, and hindgut are all differentiated for their specific roles in digestion and nutrient absorption. A chicken’s digestive system includes a crop, gizzard, proventriculus, ventricululs, and caeca as distinctive digestive organs compared to a human. The crop is mainly for food storage, the proventriculus/gizzard is similar to the stomach where a majority of food breakdown occurs, the ventriculus is similar to the small intestine where it mechanically digests food, and the ceca are pouches for absorption and food fermentation.
Embryonic gut development begins fore gut extending caudally through the endoderm. First closure of an intestine is the post-umbilical gut in the tail bud. By then end of day 3, the umbilicus begins to close towards the pancreatic bud. On day 4 a short and narrow colorectal region is now apparent.
There is much rotation and displacement of the gut throughout development that is best described step-by-step through the work of Bridget R. Southwell’s Staging of Intestinal Development of the Chick Embryo.
Below are some of her illustrations of the complex embryonic gut.
